1. Field of the Invention
The present invention relates to a tracking distance-measuring system for continuously measuring distance to, and the distance and direction of movement of, a moving target such as a running automobile.
2. Description of the Prior Art
FIG. 5 shows a distance-measuring system disclosed in Japanese Patent Publication No. 63-46363. Referring to FIG. 5, the distance-measuring system has a right optical system and a left optical system respectively comprising lenses 1 and 2 disposed a distance L apart, which corresponds to the length of a base line between the respective optical axes thereof, and image sensors 3 and 4 disposed at a distance f apart, corresponding to the focal lengths of the lenses 1 and 2 on the optical axes respectively. The image of a target 5 at a distance R from a plane including the lenses 1 and 2 are focused on the image sensors 3 and 4 respectively by the lenses 1 and 2. Then, the image sensors generate image signals. AD converters (analog-to-digital converters) 6 and 7 convert the analog image signals into proportional digital image signals, and memories 8 and 9 store the digital image signals respectively. A microprocessor 10 processes the digital image signals stored in the memories 8 and 9 to determine the distance from the target 5.
In operation, the microprocessor 10 reads a picture element signal representing a picture element at the upper left-hand corner of the image sensor 3 from the memory 8, reads a picture element signal representing a picture element signal at the upper left-hand corner of the image sensor 4 from the memory 9, and then calculates the absolute value of the difference between these two picture element signals. Then the microprocessor 10 reads picture element signals respectively representing picture elements respectively nearest to and on the right-hand side of the picture elements respectively at the respective upper left-hand corners of the image sensors 3 and 4, calculates the absolute value of the difference between the picture element signals, and then adds the absolute value to the absolute value obtained in the preceding cycle of calculation. This procedure is repeated sequentially for all the picture elements of the image sensors 3 and 4 to obtain a first value. Subsequently, the microprocessor 10 reads the picture element signal representing the picture element at the upper left-hand corner of the image sensor 3 from the memory 8, reads a picture element signal representing a picture element next to the picture element at the upper left-hand corner of the image sensor 4 to the right, and then calculates the absolute value of the difference between these picture element signals. This procedure is repeated sequentially for the differences between the picture element signal representing the foregoing picture element of the image sensor 3 and the picture element signals representing the rest of the picture elements of the image sensor 4 to obtain a second value, i.e., the accumulated total of the absolute values of the differences.
The relative dislocation of the right and left images is represented by the minimum of the accumulated total. The distance from the target 5 is determined by a formula: EQU R=f.multidot.L/n.multidot.p
where R is the distance from the target 5, n is the number of picture elements corresponding to the relative dislocation, p is the pitch of the picture elements, f is the focal length of the lenses 1 and 2, and L is the distance between the optical axes of the lenses 1 and 2 corresponding to the length of the base line.
This conventional distance-measuring system is able to measure only the distance from only a target on its optical axis. Accordingly, in measuring the distance from a moving object, the distance-measuring system must be turned according to the movement of the moving target so that its optical axis coincide with the target.